In the case of tumor surgery in the brain with a tumor in the vicinity of eloquent brain areas, that is, functional brain areas, such as, for example, in the vicinity of the motor cortex, in the vicinity of the sensorimotor centers or in the vicinity of the speech center, a surgeon is presented with the conflicting goals of, on the one hand, radically removing the tumor and, on the other hand, removing as little tissue required for healthy brain function as possible. Therefore, finding the functional brain areas as precisely as possible is of great importance.
One option for finding functional brain areas consists of detecting these areas by electrophysiological means, for example, by electrical stimulation of specific muscles and the subsequent potential measurement on the brain surface by applied electrodes. A disadvantage consists of the electrode size limiting the resolution when finding the functional tissue areas. Furthermore, it is disadvantageous, as a matter of principle, that the tissue area comes into contact with an article that is foreign to tissue, as is represented by an electrode, and so injuries can result therefrom.
U.S. Pat. No. 6,196,226 B1 or U.S. Pat. No. 5,215,095 proposes to represent functional brain areas by an optical image. Methods described in these patents comprise the tissue region being recorded during a stimulation that leads to a change in the physiological properties of the functional areas. The change in the physiological properties in turn leads to a change in the optical properties of reflected light. Therefore, a difference is formed between a stimulation image recorded during the stimulation and a comparison image recorded without stimulation in order to depict the functional areas and the functional areas are found on the basis of the difference.
A disadvantage of these methods lies in the fact that they are relatively difficult to perform since the changes connected with the functional stimulations have a weak intensity in the reflected light. Furthermore, use is made of a relatively expensive monochrome camera (black/white camera) with a high grayscale resolution and a relatively long integration time. Hence, finding functional tissue areas is relatively time intensive and expensive. Moreover, this means a relatively long time of surgery, which is unwanted for a patient as a matter of principle.